Development of an RT-LAMP Assay for the Rapid Detection of SFTS Virus

Versatility of reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) from diagnosis of early pathological infection to mutation detection in organisms

Loop-mediated isothermal amplification (LAMP) is a rapid, state-of-the-art DNA amplification technology, used primarily for the quick diagnosis and early identification of microbial infection, caused by pathogens such as virus, bacteria and malaria. A target DNA can be amplified within 30 min using the LAMP reaction, taking place at a steady temperature. The LAMP method uses four or six primers to bind eight regions of a target DNA and has a very high specificity. The devices used for conducting LAMP are usually simple since the LAMP method is an isothermal process. When LAMP is coupled with Reverse Transcription (RT), it allows direct detection of RNA in a sample. This greatly enhances the efficiency of diagnosis of RNA viruses in a sample. Recently, the rampant spread of COVID-19 demanded such a rapid, simple, and cost-effective Point of Care Test (PoCT) for the accurate diagnosis of this pandemic. Loop-mediated isothermal amplification (LAMP) assays are not only used for the detection of microbial pathogens, but there are various other applications such as detection of genetic mutations in food and various organisms. In this review, various implementations of RT-LAMP techniques would be discussed.

Comparison of dye-based and probe-based RT-LAMP in detection of canine astrovirus

A rapid and sensitive assay is essential for reliable surveillance and diagnosis of canine astrovirus (CaAstV). In this study, two real-time reverse transcription loop-mediated isothermal amplification (RT-LAMP) assays with high sensitivity, rapidity, and reliability were developed using fluorescence dye and FRET-based assimilating probes for real-time detection of CaAstV. These assays specifically amplified the ORF2 gene of CaAstV and did not amplify any sequences from canine enterovirus. The limit of detection (LOD) of both the probe-based and dye-based RT-LAMPs was 100 copies/μL. Fluorescence signals were generated within 30 min for the lowest concentration of a standard RNA sample, which was significantly faster than that achieved by real-time fluorescence quantitative PCR (qRT-PCR) assay. When clinical samples were tested, the positive and negative agreement of the dye-based RT-LAMP assay with qRT-PCR was 87.5% (14/16) and 93.55% (29/31), respectively. The positive and negative agreement of the probe-based RT-LAMP assay with qRT-PCR was 94.11% (16/17) and 96.55% (28/29), respectively. The RT-LAMP assays developed in this study showed strong potential for use as an on-site diagnostic assay for rapid, specific, and reliable detection of CaAstV in clinical samples.

Long-Term Detection and Isolation of Severe Fever with Thrombocytopenia Syndrome (SFTS) Virus in Dog Urine

Severe fever with thrombocytopenia syndrome (SFTS) is a tick-borne infection caused by the SFTS virus (SFTSV), with a high fatality rate of approximately 30% in humans. In recent years, cases of contact infection with SFTSV via bodily fluids of infected dogs and cats have been reported. In this study, clinical and virological analyses were performed in two dogs in which SFTSV infection was confirmed for the first time in the Toyama prefecture. Both dogs recovered; however, one was severely ill and the other mildly ill. The amount of the SFTSV gene was reduced to almost similar levels in both dogs. In the dogs' sera, the SFTSV gene was detected at a low level but fell below the detection limit approximately 2 weeks after onset. Notably, the SFTSV gene was detected at levels several thousand times higher in urine than in other specimens from both dogs. Furthermore, the gene was detected in the urine for a long period of >2 months. The clinical signs disappeared on days 1 or 6 after onset, but infectious SFTSV was detected in the urine up to 3 weeks later. Therefore, it is necessary to be careful about contact with bodily fluids, especially urine, even after symptoms have disappeared.

Rapid and portable bunyavirus SFTSV RNA testing utilizing catalytic hairpin assembly coupled with lateral flow immunoassay

Severe fever with thrombocytopenia syndrome (SFTS) is a prevalent, life-threatening, emergent infectious disease. Currently, reverse transcription-polymerase chain reaction is the gold standard for diagnosing SFTS virus (SFTSV) infection, which requires sophisticated equipment and professional personnel that are frequently unavailable in most SFTS endemic rural areas. Here, we reported a simple, rapid nucleic acid amplification system that combined the catalytic hairpin assembly (CHA) with a lateral flow immunoassay (LFIA) strip-based detection method for SFTSV detection. The detection of SFTSV RNA could be realized by generation of H1-H2 hybrid duplexes labeled with biotin and digoxin, which subsequently added to the LFIA test strips containing streptavidin conjugated with Alexa Fluor 647 as well as anti-digoxin antibodies. Our CHA-based LFIA assay offered high amplification efficiency and specificity with a detection limit of 1 aM. Crucially, this method enabled stable detection of 500 copies/mL of SFTSV within 30 min using clinical serum samples. Therefore, our CHA-based LFIA approach provided a potential useful tool to facilitate early and precise diagnosis of SFTS patients in poorly resourced SFTS endemic areas.IMPORTANCESevere fever with thrombocytopenia syndrome (SFTS) is an emerging and potentially fatal infectious disease prevalent in China. Here we report a simple, rapid nucleic acid amplification system, the catalytic hairpin assembly (CHA) in conjunction with a lateral flow immunoassay (LFIA) strip-based detection method for SFTS virus detection, which demonstrated high amplification efficiency and specificity with limit of detection of 1 aM. Most importantly, we also validate our CHA-based LFIA assay using the clinical serum samples, which was fully compatible with reverse transcription-PCR results. Therefore, our strategy provides a potential useful tool to facilitate early and precise diagnosis of SFTS patients especially in poorly resourced SFTS endemic areas.

Advancements in the Worldwide Detection of Severe Fever with Thrombocytopenia Syndrome Virus Infection from 2009 to 2023

Severe fever with thrombocytopenia syndrome (SFTS) is a growing concern as an emerging tick-borne infectious disease originating from the SFTS virus (SFTSV), a recent addition to the Phlebovirus genus under the family of bunyaviruses. SFTS is typically identified by symptoms such as fever, thrombocytopenia, leukopenia, and gastrointestinal problems, accompanied by a potentially high case fatality rate. Thus, early and accurate diagnosis is essential for effective treatment and disease management. This review delves into the existing methodologies for SFTS detection, including pathogenic, molecular, and immunological technologies.

Evolution of the Probe-Based Loop-Mediated Isothermal Amplification (LAMP) Assays in Pathogen Detection

Loop-mediated isothermal amplification (LAMP), as the rank one alternative to a polymerase chain reaction (PCR), has been widely applied in point-of-care testing (POCT) due to its rapid, simple, and cost-effective characteristics. However, it is difficult to achieve real-time monitoring and multiplex detection with the traditional LAMP method. In addition, these approaches that use turbidimetry, sequence-independent intercalating dyes, or pH-sensitive indicators to indirectly reflect amplification can result in false-positive results if non-specific amplification occurs. To fulfill the needs of specific target detection and one-pot multiplex detection, a variety of probe-based LAMP assays have been developed. This review focuses on the principles of these assays, summarizes their applications in pathogen detection, and discusses their features and advantages over the traditional LAMP methods.

Accuracy of reverse-transcription polymerase chain reaction and loop-mediated isothermal amplification in diagnosing severe fever with thrombocytopenia syndrome: A systematic review and meta-analysis

Nucleic acid molecular diagnostic technology plays an important role in the detection of severe fever with thrombocytopenia syndrome (SFTS). However, no relevant reports have been published on the accuracy of reverse-transcription polymerase chain reaction (RT-PCR) and reverse-transcription loop-mediated isothermal amplification (RT-LAMP) in the diagnosis of SFTS. Thus, we conducted a meta-analysis and systematic review to evaluate the accuracy of the two methods. On June 19, 2022, we comprehensively searched the PubMed, Embase, Cochrane Library, Web of Science, Scoups, Ovid, Proquest, China National Knowledge Infrastructure Database, Wan Fang Data, Traditional Chinese Medicine Database (Sinomed), VIP Database, and Reading Showing Database for articles on nucleic acid diagnostic techniques, such as RT-PCR and RT-LAMP, used to diagnose SFTS. Statistical analysis was performed using STATA 14.0 and Meta-Disc 1.4. Sixteen articles involving 2942 clinical blood samples were included in the analysis. RT-PCR and RT-LAMP were used as index tests, whereas RT-PCR or other detection methods were used as reference standards. The pooled values for the sensitivity, specificity, positive and negative likelihood ratios of the RT-PCR test were 0.97 (95% confidence interval [CI]: 0.92-0.99), 1.00 (95% CI: 0.98-1.00), 483.87 (95% CI: 58.04-4033.76), and 0.03 (95% CI:0.01-0.08), respectively. Those for the RT-LAMP test were 0.95 (95% CI: 0.91-0.97), 0.99 (95% CI: 0.93-1.00), 111.18 (95% CI: 13.96-885.27), and 0.05 (95% CI: 0.03-0.09), respectively. Both RT-PCR and RT-LAMP have high diagnostic value in SFTS and can be applied in different scenarios for laboratory confirmation or on-site screening.

Dual-gene detection in a single-tube system based on CRISPR-Cas12a/Cas13a for severe fever thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease, which is caused by severe fever with thrombocytopenia syndrome virus (SFTSV). The disease results in high mortality and increased morbidity and threatens global public health. Rapid detection of SFTSV is crucial for epidemic prevention in low-resource settings. Here we developed deployable, sensitive and rapid detection methods based on CRISPR/Cas12a or Cas13a technologies. The CRISPR/Cas12a-based detection assay could stably detect the SFTSV L or M genes at 10 cp/μl. The Cas13a-based method could detect the L gene as low as 0.75 cp/μl. For point-of-care testing, we combined fluorescence visualization and lateral flow detection with CRISPR/Cas-based assays. Furthermore, using the orthogonal DNA/RNA collateral activity of the Cas12a/Cas13a system, we present the dual-gene detection platform for SFTSV, which can simultaneously detect the L and M genes in a single tube. Based on the dual-gene detection, we designed multiplexed test strips to detect SFTSV. All our methods were initially validated using 52 clinical samples, showing 100% sensitivity and specificity. These new CRISPR/Cas-based detection methods are promising candidates for on-site detection of SFTSV.

Development of monoclonal antibody based IgG and IgM ELISA for diagnosis of severe fever with thrombocytopenia syndrome virus infection

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Developing a multiplex loop-mediated isothermal amplification assay (LAMP) to determine severe fever with thrombocytopenia syndrome (SFTS) and scrub typhus

Severe fever with thrombocytopenia syndrome (SFTS) and scrub typhus are endemic zoonotic diseases that pose significant public health threats in East Asia. As these two diseases share common clinical features, as well as overlapping disease regions, it is difficult to differentiate between SFTS and scrub typhus. A multiplex reverse-transcription loop‑mediated isothermal amplification (RT-LAMP) assay was developed to detect large segments and GroES genes for SFTS virus (SFTSV) and Orientia tsutsugamushi (OT). The performance of the RT-LAMP assay was compared and evaluated with those of commercial PowerChek™ SFTSV real-time PCR and LiliF™ TSUTSU nested PCR for 23 SFTS and 12 scrub typhus clinical samples, respectively. The multiplex SFTSV/OT/Internal control (IC) RT-LAMP assay showed comparable sensitivity (91.3%) with that of commercial PowerChek™ SFTSV Real-time PCR (95.6%) and higher sensitivity (91.6%) than that of LiliF™ TSUTSU nested PCR (75%). In addition, the multiplex SFTSV/OT RT-LAMP assay showed 100% specificity and no cross-reactivity for blood from uninfected healthy patients and samples from patients infected with other fever viruses. Thus, the multiplex SFTSV/OT/IC RT-LAMP assay could serve as a useful point-of-care molecular diagnostic test for SFTS and scrub typhus.